In processes for molding thin-walled plastic shells, a resin material is fed through an opening in a powder box to a mold surface of a mold box. Generally, the mold box and powder box are operatively connected such that the mold surface of the mold box is brought into close proximity of the opening in the powder box. The resin material is fed over the mold surface of the heated mold box and is melted into a molten resin film. The film is cooled to obtain the thin-walled plastic shell and is removed from the mold surface.
Currently, this molding process is accomplished with the powder box and mold box sealing where the two units meet; that is, at the top of the liner about the opening of the powder box and near the termination of the run off of the mold surface. This process allows the powder resin to contact the surface areas of the mold where such contact is not desired, causing waste and necessitating trimming of the finally formed part. Other methods known in the art of blocking this exposure, such as by using various insulating materials on the mold surface, still pose the problem of having to adopt special impacting and/or cooling, and/or brushing methods to keep them clean.
For example, the U.S. Pat. No. 4,790,510 to Takamatsu et al, issued Dec. 13, 1988, discloses a slush mold apparatus and method for molding film moldings such as surface coverings of interior parts of automotive vehicles. The powder box includes a skirt portion connected thereto having a lower edge which contacts the mold surface about its periphery. The skirt is a solid member which must be uniquely adapted to each unique mold surface configuration.
The present invention provides an apparatus and method for sealing at the mold about the actual periphery of the thin-wall shell which is made. Accordingly, the present apparatus and method generate little or no waste and trimming is reduced. Further, the present invention provides an apparatus and method for providing such a seal between the opening of the powder box and the periphery of the mold surface which can project into deep molds that cannot be reached by powder box elevation travel. Such deep mold surfaces can be cut into a mold box such that common mold box peripheries cannot extend into the mold surface to contact the periphery of the mold surface about the shell to be formed. The present invention provides an apparatus and method for perfecting such a seal in deep molds as well as in more shallow molds. Such a device can be adapted for both deep and shallow molds such that a single device is not limited to either the deep or shallow mold use.